Aux 1 Unit 15 Q6

1 / 10

Why is it important to protect against single phasing in a motor starter circuit?

A) To increase the motor’s operating speed

C) To increase the power output of the motor

D) To allow the motor to run on fewer phases

B) To prevent severe damage to the motor, reduce maintenance costs, and ensure reliable operation

2 / 10

What could happen to the motor if single phasing occurs while the motor is under load?

C) The motor will operate with increased power

B) The motor may stall and overheat, leading to insulation damage or even a complete motor failure

A) The motor will run more efficiently

D) The motor will automatically repair the fault

3 / 10

What is a long-term effect of single phasing on a motor if the condition is not corrected?

B) The motor’s lifespan will be significantly reduced due to continuous overheating and stress on the windings

D) The motor will switch to a two-phase system permanently

A) The motor will become more energy-efficient

C) The motor will increase its speed gradually

4 / 10

What is a common cause of single phasing in a three-phase motor system?

C) The motor being too small for the load

D) The motor being operated at a lower speed

B) A fault or disconnection in one of the supply lines

A) A sudden increase in voltage

5 / 10

What does the term "single phasing" refer to in the context of a three-phase motor?

B) The loss of one phase in a three-phase supply, causing the motor to operate on only two phases

A) The motor running at twice its normal speed

D) The motor being switched off automatically

C) The motor operating on a single-phase power supply instead of three-phase

6 / 10

What is the immediate effect on a motor’s performance when single phasing occurs?

B) The motor continues to run but with reduced torque and increased vibration

D) The motor switches to a single-phase operation smoothly

C) The motor speed increases

A) The motor operates more efficiently

7 / 10

How does a phase failure relay protect the motor from single phasing?

B) It automatically resets the motor after a fault

A) It increases the motor's speed

D) It increases the current in the remaining phases

C) It detects the loss of a phase and trips the motor to prevent it from running under single phasing conditions

8 / 10

Which device is commonly used to protect a motor against single phasing?

C) Temperature sensor

D) Speed controller

A) Over-voltage relay

B) Phase failure relay (also known as a phase loss relay)

9 / 10

In addition to a phase failure relay, what other protective measure can be implemented to guard against single phasing?

A) Install a current monitoring relay to detect imbalances in the motor’s current

C) Use a larger motor

B) Increase the motor’s speed during operation

D) Decrease the load on the motor

10 / 10

How does single phasing affect the current in the remaining two phases of a three-phase motor?

C) The current in the remaining two phases increases, potentially leading to overheating

D) The current becomes zero in both phases

A) The current decreases significantly

B) The current remains the same

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